Epigenetic modification of ferroptosis by non-coding RNAs in cancer drug resistance

The development of drug resistance remains a major challenge in cancer treatment. Ferroptosis, a unique type of regulated cell death, plays a pivotal role in inhibiting tumour growth, presenting new opportunities in treating chemotherapeutic resistance. Accumulating studies indicate that epigenetic modifications by non-coding RNAs (ncRNA) can determine cancer cell vulnerability to ferroptosis. In this review, we first summarize the role of chemotherapeutic resistance in cancer growth/development. Then, we summarize the core molecular mechanisms of ferroptosis, its upstream epigenetic regulation, and its downstream effects on chemotherapeutic resistance. Finally, we review recent advances in understanding how ncRNAs regulate ferroptosis and from such modulate chemotherapeutic resistance. This review aims to enhance general understanding of the ncRNA-mediated epigenetic regulatory mechanisms which modulate ferroptosis, highlighting the ncRNA-ferroptosis axis as a key druggable target in overcoming chemotherapeutic resistance.


Background
Cancer, after cardiovascular disease, is ranked as the second leading cause of death worldwide [1].Approximately twenty million new cancer cases were diagnosed in 2020.Lung, prostate, liver, colorectal, and stomach cancers are the most common cancers among men, while breast, colorectal, thyroid, lung, and cervical cancers are common in women [2].Surgical resection, chemotherapy, immunotherapy, radiotherapy, and targeted therapies are usually used in cancer treatment [3,4].The use of chemotherapy, molecular targeted inhibitors, and immune checkpoint inhibitors (ICIs) represents an optimal strategy for cancer therapy [5].Unfortunately, chemotherapeutic resistance or drug resistance continues to be a major problem facing current cancer research and the principal limiting factor to achieving remission in patients with cancer [6][7][8].Drug resistance is a continual foe when trying to maximize the likelihood for remission, and is mainly responsible for tumor metastasis, local recurrence, and poor prognosis, which leads to treatment failure and inevitable death [6][7][8][9].Therefore, it is desirable to elucidate the resistance mechanisms in tumor cells during treatment.Elucidating the mechanisms underlying drug resistance and hunting for effective strategies to overcome drug resistance have long been unmet urgent needs in cancer treatment [10][11][12].
Ferroptosis, a novel form of iron-dependent lipid peroxidation mediated regulated cell death (RCD) in cellular membranes, has recently been shown to functions as a dynamic tumor suppressor in cancer development, highlighting regulating ferroptosis can be utilized as an interventional target for tumor treatment [13][14][15][16][17]. Ferroptosis has also been recognized as a vital RCD triggered by chemotherapy, immunotherapy, radiotherapy, and targeted cancer therapies, partly mediating the tumour killing effects of chemotherapy [18][19][20][21][22].In the past decade, mounting evidence has uncovered that ferroptosis leads to tumour growth suppression.Importantly, the induction of ferroptosis has been demonstrated to overcome cancer drug resistance [23][24][25][26][27][28].Therefore, delineating the comprehensive molecular complexities of regulating ferroptosis may provide novel insights to create more effective therapeutic strategies to overcome chemotherapeutic drug resistance.
Major mechanisms mediating drug resistance include: tumor dynamics and intracellular genetic instability due to mutations, increased escape from cell death, alterations in non-coding RNA (ncRNA) expression, or epigenetic abberations [29].Non-coding RNAs (ncRNAs) are functional transcripts having no or limited proteincoding potential [30].ncRNAs are being increasingly recognized as vital regulatory modulators of ferroptosis [31][32][33][34][35][36][37].Emerging evidence has shown that ncRNAs regulate ferroptosis in cancer drug resistance and dictate the sensitivity of cancer cell to drugs.However, the machinery underlying the epigenetic modification of ferroptosis by ncRNAs in chemotherapeutic resistance is lacking.
In this review, we first summarize the role of chemotherapeutic resistance in cancer growth/development.Then, we summarize the core molecular mechanisms of ferroptosis, its upstream epigenetic regulation, and its downstream effects on chemotherapeutic resistance.Finally, we review recent advances in understanding how ncRNAs regulate ferroptosis and from such modulate chemotherapeutic resistance.This review aims to enhance general understanding of the ncRNA-mediated epigenetic regulatory mechanisms which modulate ferroptosis, highlighting the ncRNA-ferroptosis axis as a key druggable target in overcoming chemotherapeutic resistance.

Cancer drug resistance and cancer relapse
Drug resistance manifests most commonly as local or distant disease recurrence, and remains a looming foe against curative treatment, being the main culprit of treatment failure and remission [38].Cancer drug resistance can be secondary (acquired), which develops after exposure of tumor cells to chemotherapy, or primary (intrinsic) resistance, which is tumor specific due to genetic aberrations [38].Primary resistance is characterized by a lack of clinical response to initial therapy, and can stem from factors such has tumor heterogeneity, pre-existing genetic mutations, and activation of intracellular defense pathways, all of which potentiate therapy resistance through altering drug targets, desensitizing drug pharmacodynamics, activating oncogenic pathways, facilitating DNA repair, as well as activating survival pathways, thereby conferring evasion of cancer cells to the cytotoxic effects of treatments [6,10,39].
Secondary drug resistance develops during treatment of tumors which were initially sensitive and clinically responsive [38].Secondary drug resistance may arise from the Darwinian selection of rare pre-existing resistant clones within the heterogeneous tumor cell population [29,40].Secondary drug resistance can result from mutations arising during treatment, as well as through various other adaptive responses, such as activation of alternative compensatory signaling pathways and enhanced expression of the therapeutic target [7].
Drug resistance is also governed by genetic, epigenetic, proteomic, metabolic, or the TME, all of which confer cancer cells with the ability to survive under unfavorable conditions [39].A diverse range of molecular mechanisms have been implicated in drug resistance.The mechanisms underlying drug resistance are multifactorial, often mixed between intrinsic (innate) and extrinsic (acquired) factors [39].The key determinants of and various mechanism underlying cancer drug resistance includes: tumor heterogeneity, physical barriers, tumor burden, growth kinetics, the immune system, alterations in drug metabolism and mutation of drug targets, increased rates of drug efflux [41][42][43][44]; tumor intracellular genetic instability, tumor dynamics due to mutations [45]; enhanced escape from cell death [46]; the inactivation of downstream death signaling pathways, the activation of survival signaling pathways [47,48]; epigenetic changes, the influence of the local tumor microenvironment [49][50][51]; and alterations in microRNA (miR) expression [52,53].The presence of cancer stem cells, which are intrinsically resistant to many therapeutic approaches has been attributed to treatment failure in certain settings [54].Moreover, mounting evidence has recognized molecular and genetic heterogeneity can contribute substantially to resistance in many tumors [55].Furthermore, the induction of epithelial -to-mesenchymal transition (EMT) [56,57], intercellular communication with stromal and immune cells [58][59][60], escape from immune surveillance [6,61], alterations in intracellular drug concentration [62][63][64][65], and metabolic alterations [66][67][68] are other mechanisms implicated in cancer drug resistance.
In the enzymatic LPO pathway, Fe 2+ functions as an essential cofactor for ALOXs and POR to enhance the activity of these iron-dependent peroxidases, in which LOXs initiate the dioxygenation of PUFA-PLs in membrane [99,100].In this enzymatic processes, ACSL4 catalyzes the ligation of free PUFAs with CoA to generate PUFA-CoAs, which are subsequently re-esterified and incorporated into PLs by LPCAT3 to form PUFA-PLs [85,86,101].Then PORs and ALOXs peroxidate the incorporated PUFA-PLs to generate PUFA-PLs hydroperoxides (PUFA-PL-OOH) or peroxidated PUFA-PLs under the help of labile iron and O 2 [74,88,92].The detailed lipid resources for ferroptosis is reviewed by Tang's group [13].
The second mechanism underlying iron governs ferroptosis by initiating the non-enzymatic Fenton reaction for the direct peroxidation of PUFA-PLs [84].The Fenton reaction catalyzes and converts hydrogen peroxide(H 2 O 2 ) to hydroxyl radical (HO • ), a highly mobile water-soluble form of ROS.In this nonenzymatic LPO pathway, PUFA-PLs can react with ROS (such as LO • or HO • ) to produce lipid hydroperoxides through the Fenton reaction, thereby triggering LPO [102][103][104].First a hydrogen radical from a PUFA is abstracted by one to yield a lipid radical (L • ), which rapidly reacts with molecular oxygen (O 2 ) to produce a lipid peroxyl radical (LOO • ).Subsequently, LOO • abstracts a hydrogen radical from an adjacent PUFA to produce a lipid hydroperoxide (LOOH), which is converted to an alkoxyl radical (LO • ) in the presence of Fe 2+ .Subsequently, another lipid radical chain reaction is initiated by LO • reacts with an adjacent PUFA.This iron-dependent oxygen-catalyzed oxidation process result in membrane destruction and cell death when the ferroptosis defense systems fail to keep LPO in check [98].

Ferroptosis defense mechanisms
Normally, continuous activity of coupled enzyme-metabolite systems, which inhibit the accumulation of lipid peroxides in the membrane to toxic levels, prevent ferroptosis.These cellular antioxidant systems constitute the ferroptosis defense systems to directly neutralize lipid peroxides [69].More recently, GPX4-dependent or -independent ferroptosis surveillance pathways with specific subcellular localizations have been identified.

GPX4-GSH axis
The GPX4-GSH axis is the first discovered well-defined ferroptosis defense system [20,105].GPX4 belongs to the GPX protein family and has been identified as a key inhibitor of ferroptosis by preventing lipid hydroperoxide accumulation in most cells [14,[106][107][108][109].GPX4 has three isoforms with distinctive subcellular localizations, namely mitochondrial, cytosolic, and nuclear GPX4.Both cytosolic and mitochondrial GPX4 are vital to suppress ferroptosis in different subcellular compartments, while the nuclear GPX4 regulates ferroptosis remains to be studied [72].GPX4 is a lipid repair enzyme [110,111], which converts and reduces reactive PUFA phospholipid hydroperoxides (PUFA-PL-OOH) to non-reactive and non-lethal PUFA phospholipid alcohols (PUFA-PL-OH), concomitantly oxidizing two reduced glutathiones (GSH) into an oxidized glutathione (GSSG) [112,113].GPX4 functions closely with the cystine/glutamate antiporter System Xc − , which consists of solute carrier family 3 member 2 (SLC3A2) and SLC7A11(also known as xCT) [81].xCT functions as the transporter subunit of system Xc − , which imports extracellular cystine and exports intracellular glutamate to biosynthesize reduced glutathione (GSH) [114,115].xCT-mediated uptake of extracellular cystine is promptly reduced to cysteine under the help of NADPH (nicotinamide adenine dinucleotide phosphate) in the cytosol.

FSP1-CoQH 2 system
The ferroptosis suppressor protein 1 (FSP1)-Ubiquinone (coenzyme Q 10 or CoQ 10 ) axis was identified as the second endogenous mechanism to inhibit LPO and ferroptosis.FSP1 functions to halt ferroptosis in a pathway independent of GPX4.FSP1 is localized to the plasma membrane and acts as a NADPH-dependent CoQ reductase to convert CoQ 10 to its reduced form, ubiquinol (CoQH 2 ), which acts as a lipid-soluble antioxidant to prevent LPO and suppress ferroptosis in cellular membranes [116][117][118].FSP1 also inhibits ferroptosis by repairing plasma membrane damage, activating the endosomal sorting complex required for transport III (ESCRT-III) complex [119,120].

GCH1-BH 4 system
The GTP cyclohydrolase 1(GCH1)-tetrahydrobiopterin (BH 4 ) axis is identified as the second GPX4-independent ferroptosis defense system which inhibits LPO [121,122].GCH1 produces BH 4 , an endogenous metabolite and radical-trapping antioxidant.BH4 functions as a cofactor for aromatic amino acid hydroxylases and analogously to CoQ10 prevents LPO [121,122].GCH1 prevents ferroptosis by generating BH4 or causing remodeling of the lipid membrane environment to increase the abundance of reduced CoQ10, depleting PUFA-PLs which ferroptosis [16].

SC5D-7-DHC axis
Two groups identified the lathosterol oxidase (SC5D)-7 -dehydrocholesterol(7-DHC) axis as an novel ferroptosis inhibitor in 2024 [125,126].They reported that 7-DHC functions as a natural inhibitor of ferroptosis.7-DHC is generated in the endoplasmic reticulum found on the mitochondria and cell membrane in the cholesterol synthesis pathway, which includes the intermediates of zymosterol/lathosterol and the enzymes EBP, SC5D and DHCR7.7-DHC absorbs radicals to prevent LPO in both the mitochondria and plasma membrane by diverting the peroxidation pathway from phospholipids, thus attenuating ferroptosis.

Core mechanism of epigenetic modification
Epigenetics, a reversible and dynamic process, regulates gene expression without altering the DNA sequence [127,128].There exist four major mechanisms of epigenetic modification: DNA methylation, histone modification, chromatin structure regulation, and regulation of ncRNA [127][128][129][130][131]. Histone modification, DNA methylation, and ncRNA regulation are common well-studied epigenetic regulatory mechanisms [4].The histone subunit in the nucleosome has a tail with specific amino acids for covalent posttranslational modifications (PTMs), such as ubiquitination, phosphorylation, SUMOylation, glycosylation, methylation, and acetylation, among others [132][133][134][135].Many classes of proteins that mostly have enzymatic activities mediate epigenetic regulation of gene expression.Four classes of epigenetic regulators that include 'writers' , 'erasers' , 'readers' , and 'remodelers' , which constitute the molecular component of the epigenetic regulators of DNA methylation, histone modifications and chromatin structure [129,136].The erasers and writers remove and add epigenetic marks, respectively.The remodelers modulate the chromatin state, and the readers recognize specific epigenetic marks [127].There are approximately 1000 epigenetic regulators in mammals.The progressive accumulation of cell-intrinsic genetic and epigenetic changes result in tumorigenesis [137,138].

Epigenetic modification of ferroptosis by ncRNAs in cancer
Increasing evidence has shown that the dysregulation of epigenetic modifications induces disease onset and progression via aberrant gene expression, protein signatures, and malignant phenotypes [139][140][141].ncRNAs are being increasingly recognized as vital regulatory mediators of ferroptosis.Emerging evidence indicates that epigenetic modification affects ferroptosis at gene, transcriptional, posttranscriptional, and posttranslational levels.Targeting the epigenetic and posttranslational modifications which regulate ferroptosis is expected to provide a new direction for the treatment of cancer [130,142].Recently, ncRNAs have been shown to regulate ferroptosis via modulating iron metabolism, mitochondrial-related proteins, glutathione metabolism, and LPO [31][32][33][34][35][36][37].In cancer, ncRNAs regulate ferroptosis by regulating genes which encode ferroptosis defense systems or ferroptosispromoting factors [34].ncRNAs regulate ferroptosis in cancer cells by affecting iron metabolism, lipid metabolism, the SLC7A11/GSH/GPX4 network, glutamine metabolism, and KEAP1/Nrf2 pathway among others [34].

Regulating ferroptosis by ncRNAs in cancer drug resistance
ncRNAs are functional transcripts with limited or no protein-coding ability [30].microRNA (miRNA), long non-coding RNAs (lncRNA), and circular RNA (cir-cRNA) are the major classes of regulatory ncRNAs among others, which exert their functions through various modes of action [143][144][145][146] (Fig. 3).ncRNAs contribute to regulate cellular behaviors and signal transduction, as well as in the pathogenesis of diseases, including cancer [147][148][149][150]. ncRNAs, particularly miRNAs, lncRNAs, and circRNAs, are widely identified as pervasive regulators of multiple cancer hallmarks such as proliferation, invasion, apoptosis, metastasis, and genomic instability.Accumulating evidence has revealed that dysregulated epigenetic regulation by ncRNAs contributes to cancer therapy resistance, including chemotherapy, targeted therapy, immunotherapy, and radiotherapy, by rewiring essential signaling pathways [151][152][153][154][155][156][157].Thus, targeting ncRNAs might be a potential regimen to modulate cancer drug resistance [158].Accumulating evidence has revealed that dysregulated epigenetic regulation by ncRNAs contributes to tumor drug resistance through regulating ferroptosis.In the following sections, we will review recent advances in uncovering the mechanisms underlying ncRNAs regulate ferroptosis pathways in cancer drug resistance.

The regulatory role of miRNAs in modulation of ferroptosis in cancer drug resistance Drug resistance to chemotherapy
Downregulated expression of miR-324-3p was observed in cisplatin-resistant A549 (A549/DDP) cells [159] (Fig. 4 and Table 1).Overexpression of miR-324-3p reverses cisplatin resistance.miR-324-3p targets GPX4, and overexpression of GPX4 reverses miR-324-3p-mediated increased sensitivity of A549/DDP cells to cisplatin [159].miR-324-3p facilitates cisplatin -induced ferroptosis in the A549/DDP cells.RSL3, the GPX4 inhibitor, mimics the effects of overexpressed miR-324-3p in increasing the sensitivity of the cisplatin-resistant cells to drug [159].Together, miR-324-3p reverses cisplatin resistance by inducing ferroptosis via inhibiting GPX4 in NSCLC.Upregulated miR-4443 levels were observed in cisplatin-resistant tumor-released exosomes.Exosomes mediated the transfer of miR-4443 to sensitive cells to confer chemoresistance in recipient cells [160].The overexpression of miR-4443 in sensitive cells enhances resistance to cisplatin, silencing miR-4443 was found to overcome cisplatin resistance.Methyltransferaselike 3 (METTL3) was identified as a target gene of miR-4443 [160].miR-4443 promotes resistance to cisplatin by inhibiting ferroptosis via upregulation of FSP1 in an m 6 A-dependent manner via METLL3 [160].miR-6077 works as a key driver of cisplatin/pemetrexed (CDDP/ PEM) resistance in lung adenocarcinoma(LUAD) [161].miR-6077 promotes LUAD resistance to CDDP/PEM via CDKN1A/cell cycle arrest and KEAP1/ferroptosis pathways.Overexpression of miR-6077 decreases the sensitivity of LUAD cells to CDDP/PEM in vitro and in vivo.3 Molecular synthesis and functionality of miRNAs, lncRNAs, and circRNAs.(a) miRNA is synthesized by RNA polymerase II/III and begins as primary miRNA (pri-miRNA), which is then processed by Drosha/DGCR8 to produce precursor miRNA (pre-miRNA).pre-miRNA is exported out of the nucleus by Exportin E and is further processed by TRBP/DICER to produce duplex miRNA.One strand of duplex miRNA is degraded while the other "mature" strand is loaded into AGO2 to form RISC, which may participate in mRNA deadenylation, degradation, translation repression, and bind to miRNA response elements (MRE).Mature mRNA may also activate TLRs, interact with non AGO2 proteins, or directly modify transcriptional activity.(b) lncRNA is synthesized by RNA polymerase II/III/IV and begins as premature RNA that must be spliced.Spliced RNA forms secondary/tertiary structure and binds to proteins, forming paraspeckle assemblies, regulation transcriptional activity, or enters the cytosol.Within the cytosol lncRNA may bind to mRNA, be translated into protein via open reading frames (ORF), or be inhibited by loaded RISC.(c) circRNA is synthesized by RNA polymerase II and begins as premature RNA that back-splices.Mature circRNA leaves the nucleus and enters the cytosol where it may bind proteins, be translated via ORFs into protein, or via MREs interacts with loaded RISC CDDP/PEM induces cell death by upregulating CDKN1A and KEAP1, which activates cell-cycle arrest and ferroptosis, respectively [161].miR-6077 targets KEAP1 and CDKN1A.miR-6077 enhances chemoresistance through CDKN1A-CDK1-mediated cell-cycle arrest and inhibits ferroptosis via KEAP1-Nrf2-SLC7A11/NQO1 in vitro and in vivo [161].GMDS-AS1 and LINC01128 increases the sensitivity of LUAD cells to CDDP/PEM by sponging miR-6077.Collectively, these results suggest miR-6077 functions as an oncogene to promote cisplatin/pemetrexed resistance via CDKN1A/cell cycle arrest and KEAP1/ferroptosis pathways in NSCLC [161].Propofol decreases cisplatin resistance by inducing GPX4mediated ferroptosis by the miR-744-5p/miR-615-3p axis in NSCLC.Propofol inhibits GPX4 transcription by upregulating miR-744-5p/miR-615-3p [162].Increased GPX4 or decreased miR-744-5p /miR-615-3p alleviates the inhibitory effect of propofol on chemoresistance to cisplatin [162].Increased Aurora kinase A (AURKA) and decreased miR-4715-3p were observed in upper gastrointestinal adenocarcinoma (UGC) [163].miR-4715-3p binds to and downregulates AURKA, leading to chromosomal polyploidy, G2/M delay, and cell death [163].miR-4715-3p increases UGC cell death and enhances cisplatin sensitivity through inducing ferroptosis via inhibition of GPX4 [163].

The regulatory role of LncRNAs in modulation of ferroptosis in cancer drug resistance Drug resistance to chemotherapy
Increased expression of lncRNA ITGB2-AS1 was observed in cisplatin-resistant NSCLC cells and NSCLC patients, which was positively correlated negative repression of ferroptosis [176](Fig.5 and Table 2).Silencing lncRNA ITGB2-AS1 suppresses resistant cell proliferation and promotes cell apoptosis and ferroptosis.LncRNA ITGB2-AS1 increases NAMPT expression by binding to FOSL2, thereby inhibiting p53 expression.Silencing lncRNA ITGB2-AS1 inhibits cisplatin resistance in NSCLC in vivo [176].Together, these results suggest that lncRNA ITGB2-AS1 enhances resistance to cisplatin by suppressing p53-mediated ferroptosis via activation of the FOSL2 /NAMPT axis in NSCLC [176].
Increased expression of lncRNA MACC1-AS1 interacts with and stabilizes the protein kinase STK33 to prevent its ubiquitination and subsequent degradation, leading to its cytoplasmic accumulation, thereby activating GPX4 to inhibit gemcitabine-induced cellular oxidative damage [181].The decreased expression of lncRNA ATXN8OS was observed in U251TR cell lines.LncRNA ATXN8OS suppresses malignant phenotypes by enhancing ferroptosis in glioma in vitro [182].LncRNA ATXN8OS inhibits the resistance of glioma to temozolomide in vitro and in vivo [182].LncRNA ATXN8OS stabilizes GLS2 mRNA by recruiting adenosine deaminase acting on RNA (ADAR).GLS2 inhibits the resistance of glioma to temozolomide in vitro and in vivo [182].GLS2 enhances ferroptosis and inhibits malignant phenotypes of glioma in vitro.Together, these results suggest that LncRNA ATXN8OS inhibits temozolomide -resistance in glioma by inducing ferroptosis via ADAR-mediated stabilization and upregulation of GLS2 mRNA [182].Fanconi anemia complementation group D2 (FANCD2) and CD44 are identified as temozolomide resistance-related genes.Silencing FANCD2 and CD44 increases the sensitivity of cancer cells to temozolomide and promotes ferroptosis in U87 and U251 cells.Silencing lncRNA TMEM161B-AS1 inhibits cell proliferation, migration, and invasion, while enhancing glioma cell apoptosis.LncRNA TMEM161B-AS1 works as a sponge for hsa-miR-27a-3p [183].The hsa-miR-27a-3p mediates an inhibitory effect on GBM cells induced by silencing lncRNA TMEM161B-AS1.Together, these results suggest that lncRNA TMEM161B-AS1 promotes temozolomide resistance by inhibiting ferroptosis via sponging hsa-miR-27a-3p, upregulating CD44 and FANCD2 [183].Evasion of ferroptosis was found in acquired docetaxel-resistant PCa cell lines.Increased expression of lncRNA PCAT1 was observed in PCa cell lines and clinical samples with docetaxel-resistance [184].The overexpression of lncRNA PCAT1 inhibits ferroptosis by activating SLC7A11 expression and promotes docetaxel resistance, which was reversed by PCAT1 knockdown [184].LncRNA PCAT1 interacts with and stabilizes c-Myc, thereby transcriptionally upregulating SLC7A11 expression.The lncRNA PCAT1 also increases SLC7A11 expression by competing for miRNA-25-3p.

The regulatory role of CircRNAs in modulation of ferroptosis in cancer drug resistance Drug resistance to chemotherapy
Upregulated CircDTL was observed in NSCLC cells.Silencing circDTL increases the sensitivity of NSCLC cells to chemotherapeutic agents by inducing apoptosis and ferroptosis.circDTL decreases the expression of miR-1287-5p, which targets GPX4 to inhibit ferroptosis in NSCLC cells [191] (Fig. 6 and Table 3).Collectively, these results suggest that CircDTL functions as an oncogene to promote chemotherapeutic resistance by inhibiting ferroptosis via sponging miR-1287-5p to upregulate GPX4 in NSCLC [191].Silencing circSnx12 enhances the sensitivity of cisplatin-resistant ovarian cancer cells to cisplatin by activating ferroptosis in vitro and in vivo.Downregulation of miR-194-5p partially abolished these effects.circSnx12 can sponge miR-194-5p, which targets SLC7A11 [192].Collectively, these results suggest circRNA circSnx12 promotes cisplatin chemoresistance by suppressing ferroptosis via sponging miR-194-5p to upregulate SLC7A11 in ovarian cancer [192].CircHIPK3  which may be partially attributed to the inhibition of autophagy and ferritinophagy.[197] circUPF2 Hepatocellular carcinoma ↑/Oncogene Sorafenib SLC7A11 ↑Sorafenib resistance by promoting SLC7A11 expression and suppressing ferroptosis in HCC cells.[198] circ-BGN Breast cancer

Challenges and future directions for ncRNA research in cancer therapeutics
ncRNAs can function as diagnostic/predictive biomarkers or as direct therapeutic targets.[151,201].Since the first well-described lncRNA Xist [202,203] and miRNA gene lin-4 [204,205] were identified, thousands of ncRNAs have been named.Xist is responsible for X-chromosome inactivation in females [202,203].Lin-4 encodes a precursor RNA, which is processed into a short, 22-nucleotide double stranded RNA that functions as an important regulator of C. elegans development [204,205].As soon as they were discovered, even before their mechanism of action was well understood, ncRNAs were viewed from a therapeutic mentality.Over the past decade, the clinical application of RNA-based therapeutics has made great effort, employing mostly small interfering RNAs and antisense oligonucleotides, with several gaining FDA approval as noted in a previous review [206].Many RNA therapeutics are in phase II or III clinical development, including miRNA mimics and anti-miRNAs, but no lncRNA-based therapeutics have entered the clinic as noted in a previous review [206,207].Two major hurdles are seen in producing a ncRNA drug: methods needed to deliver charged nucleic acid analogs across hydrophobic cell membranes, and the rapid degradation of RNA by RNases [201].It has taken more than 40 years of painstaking work to overcome these obstacles since the initial observation showing that a 13-mer DNA oligonucleotide could sequence-specifically inhibit RSV translation and proliferation in 1978 [208,209].
Dysregulation of both types of lncRNA and miRNA has been linked to every cancer, impacting all major cancer hallmarks [210][211][212][213]. Advances in RNA biology has been fueled in large part by the development of more inexpensive and sensitive methods to sequence RNAs expressed in cells, isolating/characterizing RNAs bound to protein, DNA, and other RNAs [214].Revolutions in genome editing, multi-omics, oligonucleotide chemistry and RNA engineering are paving the way for efficient and cost-effective ncRNA-focused drug discovery pipelines.Various RNA-based therapies, including small interfering RNAs (siRNAs), antisense oligonucleotides (ASOs), miRNA sponges, short hairpin RNAs (shRNAs), miRNA mimics, ASO anti-microRNAs (antimiRs), therapeutic circular RNAs (circRNAs), and CRISPR-Cas9-based gene editing have been developed (see recent excellent review [215,216].All these therapeutics are either ASOs or siRNAs that downregulate specific gene, or ASOs that target pre-mRNA splicing.
In ncRNA research, bioinformatics tools can efficiently identify and predict potential targets of ncRNA.MNDR, miRDB MicroRNA Target Prediction Database, DIANA tools, and other tools are typically based on the interaction patterns between RNA and DNA, RNA, or proteins.Through sequence alignment, structural prediction, expression profiling analysis, and other methods, candidate genes or proteins that may bind to ncRNA are screened.For the study of ferroptosis, bioinformatics can help us identify ncRNA targets related to iron metabolism, lipid peroxidation, antioxidant systems, and more.For example, by comparing the sequence similarity between ncRNAs and known ferroptosis regulatory genes, it is possible to predict which ncRNAs may affect their expression levels by directly binding to the mRNA of these genes, thereby regulating the ferroptosis process.Systems biology methods can reveal how ncRNAs form complex regulatory networks through interactions with other molecules such as mRNA, proteins, metabolites, etc., collectively affecting the fate of cell ferroptosis.By constructing ncRNA, mRNA, and ncRNA protein interaction networks, systems biology can identify key ncRNA nodes involved in ferroptosis and how they synergistically promote or inhibit ferroptosis by regulating multiple downstream targets.In addition, by combining metabolomics, proteomics, and other omics data, systems biology can further reveal the metabolic and signaling pathways of ncRNA in ferroptosis, providing important clues for a deeper understanding of its molecular mechanisms.

Conclusions and perspectives
In this review we aimed to summarize the upstream role of ncRNA epigenetic mechanisms on downstream ferroptosis and chemotherapeutic resistance.This review will improve the insights into the epigenetic regulatory mechanisms by ncRNA on ferroptosis in cancer drug resistance, providing an important understanding on how targeting ncRNAs implicated in ferroptosis can be used to prevent chemoresistance.
Research on the upstream ncRNA-mediated epigenetic modification of ferroptosis in chemoresistance still in its infancy.Much is needed to bridge the gap to provide satisfactory biological outcomes.First, more research is needed to further elucidate the discrete mechanisms by which ncRNAs modulate ferroptosis.Second, research is needed to identify which small molecule compounds can revert aberrant ncRNA-mediated epigenetic inhibition of ferroptosis.Third, ncRNAs participate in a crosstalk between ferroptosis and other regulated cell death in cancer [217].It is still unknown how ncRNAs the enhance/inhibit ferroptosis impact other mechanisms of regulated cell death, such as cuproptosis [202].Fourth, ncRNAs directly regulate ferroptosis by modulating ferroptosis-related proteins or enzymes involved in antioxidant defense, iron metabolism, and lipid metabolism.However, it us unknown how ncRNAs regulate ferroptosis by modulating transcription factors, such as Nrf2, the master regulator of the antioxidant response.
Taken together, emerging evidence has shown that ncRNAs regulate chemotherapeutic resistance by modulating ferroptosis.This review summarizes the regulatory roles of several types of ncRNAs in ferroptosis during chemoresistance, highlighting that ferroptosis-associated ncRNAs have immense therapeutic and diagnostic potential in chemotherapeutic resistance.

Fig.
Fig.3Molecular synthesis and functionality of miRNAs, lncRNAs, and circRNAs.(a) miRNA is synthesized by RNA polymerase II/III and begins as primary miRNA (pri-miRNA), which is then processed by Drosha/DGCR8 to produce precursor miRNA (pre-miRNA).pre-miRNA is exported out of the nucleus by Exportin E and is further processed by TRBP/DICER to produce duplex miRNA.One strand of duplex miRNA is degraded while the other "mature" strand is loaded into AGO2 to form RISC, which may participate in mRNA deadenylation, degradation, translation repression, and bind to miRNA response elements (MRE).Mature mRNA may also activate TLRs, interact with non AGO2 proteins, or directly modify transcriptional activity.(b) lncRNA is synthesized by RNA polymerase II/III/IV and begins as premature RNA that must be spliced.Spliced RNA forms secondary/tertiary structure and binds to proteins, forming paraspeckle assemblies, regulation transcriptional activity, or enters the cytosol.Within the cytosol lncRNA may bind to mRNA, be translated into protein via open reading frames (ORF), or be inhibited by loaded RISC.(c) circRNA is synthesized by RNA polymerase II and begins as premature RNA that back-splices.Mature circRNA leaves the nucleus and enters the cytosol where it may bind proteins, be translated via ORFs into protein, or via MREs interacts with loaded RISC

Fig. 4
Fig. 4 miRNA regulation of ferroptosis in cancer drug resistance.miRNAs may modify phospholipid metabolism, inhibit antiferroptotic safety measures, or directly induce ferroptosis by modifying cellular redox cycles.Cumulatively, miRNAs play a strong role in maintaining peroxyphospholipid homeostasis

Fig. 5
Fig. 5 lncRNA regulation of ferroptosis in cancer drug resistance.lncRNAs may impact antiferroptotic defense systems, proferroptotic proteins, and undiscovered targets to modify cellular peroxyphospholipid homeostasis PTEN destabilization confers oxaliplatin resistance by inhibiting ferroptosis. of gliomas through promoting ferroptosis via ADAR/GLS2 pathway.↑Malignant biological behavior of glioma cells and the resistance to temozolomide via upregulating the expression of multiple ferroptosis-related genes by sponging hsa-miRresistant prostate cancer through c-Myc/miR-25-3p /SLC7A11 Signaling; ↓ferroptosis by activating SLC7A11 expression.ferroptosis by inducing ferritin phase separation and reducing the cellular free iron content.DUXAP8 boosts sorafenib induced ferroptosis in via SLC7A11 de-palmitoylation.sorafenib resistance through promoting ferroptosis via inhibiting GPX4 by binding to miR-450b-5p.facilitates erlotinib sensitivity through inducing ferroptosis by upregulating lncRNA H19.

Fig. 6
Fig.6circRNA regulation of ferroptosis in cancer drug resistance.circRNAs may impact antiferroptotic defense systems, proferroptotic proteins, and undiscovered targets to modify cellular peroxyphospholipid homeostasis

Table 1
The regulatory role of miRNAs in modulation of ferroptosis in cancer drug resistance

Table 3
The regulatory role of circRNAs in modulation of ferroptosis in cancer drug resistance